The present invention relates to a piezoelectric transducer array for use in an ultrasonic imaging system particularly for medical applications and to an ultrasonic imaging system of an arc scan type incoporating the array.
Ultrasonic transducer arrays are currently classified under the categories of linear scan type, sector scan type and arc scan type. Conventional transducer arrays used in the arc scan type comprise an elongated piezoelectric member of a ceramic material which is formed into the shape of an arch, a plurality of electrodes arranged on one surface of the piezoelectric member, and a common electrode attached to the other surface of the piezoelectric member. The common electrode is covered by an insulative layer such as silicon rubber or the like, while the individual electrodes are covered by a layer of ferrite rubber or epoxy resin mixed with tungsten powder for purposes of damping vibrations of the piezoelectric member and adding a structual integrity thereto. The insulative layer defines a surface that is convex in the direction of propagation of ultrasonic energy to serve as a contact face with a human subject. Conventional methods for forming such a curved piezoelectric member involve deforming the piezoelectric ceramic body into the shape of an arch and then baking the arched body at an elevated temperature, or grinding the ceramic body into the shape of an arch. By comparison with a flat-type transducer array wherein no forming process is involved, the conventional convex type transducer array is disadvantageous in terms of yield. Furthermore, since the individual electrodes define with the common electrode plural regions of an electrically energized state to generate ultrasonic energy from such regions, adjacent regions tend to interfere with each other producing an abnormal sidelobe which causes the array to deviate in operating performance from the intended design parameters. Since the vibrational mode of the conventional array is of a thickness mode, the electromechanical coefficient k.sub.t is less than 0.5, a value insufficient to provide satisfactory sensitivity and frequency bandwidth characteristics.